Interstellar comet 3IATLAS nears the Sun with unusual evolution

A fast-moving interstellar comet dubbed 3IATLAS is drawing intense scrutiny from astronomers as it nears its closest approach to the Sun next month, with observers reporting rapid changes in the object’s appearance and composition and researchers debating its size and origins. The object, first identified by the ATLAS all-sky survey on July 1, is confirmed by NASA to have come from outside the solar system and is currently passing through the inner planets without posing any threat to Earth.

Observers worldwide say 3IATLAS has developed a pronounced coma and an elongating tail as solar heating increases. Amateur comet hunter Michael Jäger and colleagues reported using the total lunar eclipse to capture deep images from Namibia that show the coma shifting from a red hue to green. Harvard astrophysicist Avi Loeb suggested in a blog post that the color change could reflect a steep rise in the production of cyanide, while the ATLAS team has described the object’s "anomalous evolution" as a shift from sunlight scattering off reddened dust to the release of small, optically bright icy grains.

Scientists have also noted an unusually high ratio of carbon dioxide to water in the object’s...